1. Filed of the Invention
The present invention relates to an air-conditioner, a refrigeration unit or the like driven by a heat-pump apparatus using a scroll-compressor.
2. Description of the Related Art
A conventional heat-pump apparatus will be described with reference to FIG. 2. A compressor 100, an evaporator 210, a condenser 220, and an expansion valve 230 are connected so as to constitute a circuitry as shown in FIG. 2. A control apparatus 240 is one for controlling the rotational speed of the compressor 100, which is formed of a power conversion equipment such as an inverter. For example, in an air-conditioner as an example of a heat-pump, the control device 240 adjusts the rotational speed of the compressor 100 within an controllable range through variable control or on-off control for the operation of the compressor 100 so as to adjust the indoor temperature to a set temperature which is a control target. Further, the control device 240 carries out also adjustment to the opening degree of the expansion valve 230, and adjustment to a draft rate of air fed into the evaporator 210 or the condenser 220. Thus, the heat-pump apparatus is operated through the control of refrigerating cycle so as to gain a required refrigerating capacity, and then is operated under such control that control values are decreased so as to restrain the power consumption after the indoor temperature reaches the set temperature.
The compressor used in this heat-pump is a scroll compressor of such a type that an orbiting scroll member having a spiral wrap formed on a base plate and an non-orbiting (stationary scroll) member having a spiral wrap formed on a base plate are meshed with each other so as to define a compression chamber. In this scroll compressor, a force to separate the orbiting scroll member and non-orbiting scroll is generated by pressure within the compression chamber. Accordingly, it is required to generate a force in a direction in which both scroll members are pressed to each other, against the above-mentioned separating force.
Specifically, a backside pressure zone is formed in a side of the base plate (an end plate in other words), opposite to the compression chamber, of at least one of the orbiting and non-orbiting scrolls, and fluid pressure is introduced into the backside pressure zone in order to generate a force (pressing force) to make the orbiting and non-orbiting scrolls close to one another. In this arrangement, the backside pressure is generated by a mechanism which is designed so as to set the backside pressure to an intermediate pressure between a suction pressure and a discharge pressure, which is equal to a value obtained by a formula, (a pressure in a certain part in the heat pump apparatus, such as the suction pressure).times.(a substantially constant value)+(a substantially constant value).
As documents disclosing this type of arrangement to introduce pressure into the back pressure chamber, JP-A-7-217557 (document 1) and JP-A-64-381 (document 2) are known.
The document 1 discloses such an arrangement that the back pressure chamber and the suction side are communicated with each other thorough a pipe incorporating a pressure regulating valve and when a differential pressure becomes higher than a spring force set by a pressure regulating knob for initial setting, the valve is opened to set a differential pressure which corresponds to the spring force.
Further, the document 2 discloses such an arrangement that the back surface zone of the orbiting scroll is divided into two concentric pressure zones, high pressure being introduced into the inner zone and lower or high pressure being introduced into the outer zone in dependence upon a condition so as to change the pressing force.
In the above-mentioned document 1, the back pressure chamber induces therein a pressure corresponding to a suction pressure, so as to obtain a pressure corresponding to the once set spring force, that is, the pressure of the back pressure chamber becomes a value which is obtained by adding a pressure overcoming the spring force to the suction pressure. However, the relationship between the suction pressure and the pressure in the back pressure chamber is constant, and this document 1 fails to disclose such an arrangement that the pressure is set to a further appropriate pressure.
Further, in the above-mentioned documents 2, the pressure in the outer zone in the back pressure chamber is changed over through two stages in accordance with a high or low differential pressure, and although what is the high pressure or the low pressure is unclear, only two kinds of averaged pressures are used in the back pressure chamber. However, similar to the document 1, this document 2 also fails to disclose such an arrangement that the pressure is set to a further appropriate pressure.